RESUMO
The evolution of plants on land has produced a great diversity of organs, tissues, and cell types. Many of the genes identified as having a role in the development of such structures in flowering plants are conserved across all land plants, including in clades that diverged before the evolution of the structure in question. This suggests that novel organs commonly evolve via the cooption of existing developmental gene regulatory networks (GRNs). Although numerous examples of such cooptions have been identified, little is known about why those specific GRNs have been coopted. In this review, we discuss the properties of GRNs that may favor their cooption, as well as the mechanisms by which this can occur, in the context of plant developmental evolution. We especially focus on small RNA (sRNA)-regulated and auxin-signaling GRNs as intriguing models of regulatory network recruitment.
Assuntos
Evolução Biológica , Redes Reguladoras de Genes , MicroRNAs/metabolismo , RNA de Plantas/metabolismo , RNA Interferente Pequeno/metabolismo , Sequência de Bases , MicroRNAs/genética , Dados de Sequência Molecular , Desenvolvimento Vegetal/genética , RNA de Plantas/genética , RNA Interferente Pequeno/genéticaRESUMO
Plants generate new organs through the activity of small populations of stem cells present in specialized niches called meristems. Stem cell homeostasis is attained by dynamic regulatory networks involving transcriptional regulators, hormones, and other intercellular signals that specify cell fate and convey positional information to the apical stem cells and the organizing center located immediately below. The balance between stem cell maintenance within the shoot apical meristem (SAM) and differentiation of cells that are displaced from the niche to form new organs involves the epigenetic silencing of stem cell regulatory genes. Recent advances have identified highly conserved chromatin remodeling factors as epigenetic regulators of stem cell fate that confer plasticity in plant development and ensure the stable inheritance of repressed expression states during organogenesis. These advances reveal that common mechanisms contribute to stem cell homeostasis in plants and animals.
Assuntos
Células Vegetais , Plantas/genética , Células-Tronco/citologia , Células-Tronco/metabolismo , Epigênese Genética , Retroalimentação Fisiológica , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Homeostase , Meristema/citologia , Meristema/metabolismo , Modelos Biológicos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas/metabolismoRESUMO
Small RNAs and their targets form complex regulatory networks that control cellular and developmental processes in multicellular organisms. In plants, dorsoventral (adaxial/abaxial) patterning provides a unique example of a developmental process in which early patterning decisions are determined by small RNAs. A gradient of microRNA166 on the abaxial/ventral side of the incipient leaf restricts the expression of adaxial/dorsal determinants. Another class of small RNAs, the TAS3-derivated trans-acting short-interfering RNAs (ta-siRNAs), are expressed adaxially and repress the activity of abaxial factors. Loss of maize leafbladeless1 (lbl1) function, a key component of the ta-siRNA biogenesis pathway, leads to misexpression of miR166 throughout the initiating leaf, implicating ta-siRNAs in the spatiotemporal regulation of miR166. The spatial restriction of tasiRNA biogenesis components suggests that this pathway may act non-cell-autonomously in the meristem and possibly contributes to the classic meristem-borne adaxializing Sussex signal. Here, we discuss the key participants in adaxial/abaxial patterning and point out the intriguing possibility that organ polarity in plants is established by the opposing action of specific ta-siRNAs and miRNAs.
